Pancreatitis is associated with significant morbidity and mortality. Unfortunately, there are currently no effective therapies for this disease. This is largely because the molecular mechanisms that determine the severity of this disease remain poorly understood. Knowledge of these mechanisms has been hampered by the lack of well-defined animal models. In the current proposal, we will utilize novel transgenic animal models that we have recently developed based on acinar cell specific expression of a tamoxifen-regulated Cre recombinase that is used to activate or delete genes that directly regulate pancreatitis severity. These are the first animal models of pancreatitis in which the molecular initiating events are clearly defined. The overall aims of this proposal are to test specific mechanistic hypotheses using these unique models. Specific aim #1 involves the regulated expression of components of the NF?B signaling pathway. Despite much evidence that NF?B is a critical mediator of pancreatitis, many important questions remain about its specific actions in the disease. We will directly examine the role of NF?B by regulating the expression of molecules that will either activate (p65/relA over-expression) or inhibit (l??-? deletion or I?B? expression) NF?B specifically in pancreatic acinar cells. We will test several mechanistic hypotheses concerning the roles of acinar cell NF?B activation in the inflammatory cascade, acinar cell apoptosis and necrosis, and pancreatic regeneration associated with acute pancreatitis. Specific aim #2 is based on regulated expression of mutant active K-ras(G12V) in pancreatic acinar cells. While activated K-ras is generally associated with pancreatic cancer, we have observed that its expression in acinar cells within the pancreas of transgenic animals leads to a dramatic loss of acinar cells and abundant fibrosis resembling human chronic pancreatitis. We will utilize this unique animal model to identify the specific molecular mechanisms whereby K-ras activity causes acinar cell damage and influences stellate cells to produce fibrosis. To complement the studies in transgenic mice and to insure that the mechanisms being investigated are relevant to human disease, we will also conduct studies in vitro using viral vectors to express genes in human and rodent acinar cells. Together these studies will provide insights into the mechanisms of acute pancreatitis that have not previously been possible and which may lead to improved therapies.